AN underworld gang which planned the robbery of the Millennium Dome already had a buyer for the &#xA3;200m diamonds.

Police believe the raiders probably attempted the robbery on an order from the Russian Mafia, who in turn were acting for a wealthy collector, possibly an Arab.

The robbery might have succeeded but for painstaking and old-fashioned detective work by police officers.

They arrested the gang red-handed after they crashed through the Dome on a JCB earthmover and smashed through the armoured glass protecting the Millennium Star and its rare sister diamonds.

One robber, Robert Adams, commented ruefully, "I was only 12 inches away from pay day."

It was the Flying Squad's biggest ever operation and it was launched after a chance sighting of the gang's ringleaders at the Dome two months before.

The Dome was among a number of high security sites the Flying Squad were covertly watching after an equally daring robbery bid earlier in the year. That raid was bungled but it quickly became clear they were a sophisticated and potentially highly dangerous gang.

The Flying Squad decided to put some of Britain's most notorious criminals under surveillance and drew up a list of possible robbery targets, which included the Dome.

"We knew these people were up for the business," said Detective Chief Superintendent Jon Shatford.

"We never knew how the robbery would take place and catered for a number of options."

On November 6, 90 armed officers were moved into and around the Dome. Just around 9.30am they saw Betson driving a JCB towards the Dome. On board with him hidden under covers were Cockram, Adams and Aldo Ciarrocchi. All wore body armour and had masks.

"We had earlier discounted a JCB just charging in as it would be too dangerous," said Mr Shatford.

A party of schoolchildren from Dorset who were touring the Dome were immediately evacuated. They thinned out other tourists, but could not disturb the environment too much, as the gang might have become suspicious.

"The JCB came into sight and crashed through the gates, straight into the Dome and sped right up to the diamond vault," said Mr Shatford.

"They got out looking like terror-ists, Ciarrocchi threw smoke flares while Cockram went into the vault with a nailgun, firing it into the three-quarter-inch glass. Adams followed with sledgehammers.